From the German Auslegeschrift 3,300,666, a method is known for washing small objects. In this method, the small objects in treatment baskets are passed through the solvent in a closed vessal and washed by spraying above the level of the solvent. This method is used as a washing method and has some advantages. However, it is not suitable for removing coatings or stripping enamel from objects.
To remove the coating or strip the enamel from the objects to be treated, so-called cold enamel-stripping methods in large open tubs are known. These methods have the serious disadvantage that they are injurious to health due to vapors occurring above and in the surroundings of the immersion basins. Moreover, on removal of the objects from the tubs, adherent solvents may be released. The solvents, which run or drip from the parts, may reach the soil or underground water. Moreover, methylene chloride evaporates vary rapidly and thus additionally contaminates the air.
Moreover, the solvent may become entrained in the treated parts. There are chlorine-containing solvents in the paint residues, so that the disposal of the latter is expensive. Furthermore, only a limited use of additives, such as phenols, cresols, etc. is possible for health and environmental reasons. When the immersion baths contain about 50% sludge, the whole system must be destroyed or exchanged. Due to the more stringent demands with respect to environmental impact, this known technology has been replaced by other methods.
For example, it is known that pyrolysis may be carried out at higher temperatures. For such a pyrolysis, which may take place at temperatures around 400.degree. C., there are natural limitations with regard to the material of the objects to be treated. For example, no temperature sensitive parts, such as wood, plastics, hardened metals, thin metal sheets, light metals, nonferrous heavy metals, soldered parts, magnetized metals, etc. can be treated. As for the rest, halogen compound may occur in the hot waste gases, for example, when polyvinyl chloride or chlorinated rubber are carbonized. These acidic gases can be neutralized in so-called post-scrubbers. However, highly toxic dioxins are formed during the combustion (Seveso). These dioxins may then be found in the scrubbing water or reach the environment through the smoke stack.
A different technology consists of the cryostatic stripping of enamel at very low temperatures of about D196.degree. C. in liquid nitrogen. However, this is associated with great technical effort. The area of use is also limited, especially in the case of elastic and thin layers of enamel. Unwanted stresses may also develop, especially in the region of welded and soldered sites.
Enamel stripping by combustion is no longer possible at the present time already for environmental reasons. Even if these reasons did not exist, such a method could be used only on a limited scale, if at all.
Aside from the treatments described above, a so-called hot enamel stripping in hot alkali liquors or acids, such as sulfuric acid, is known. This treatment is dangerous; heavy metals, complexing agents and surfactants accumulate in the baths, so that, finally, there may be contamination of the environment, especially of the sewage. The extremely aggressive, corrosive vapors also contaminate the environment and affect the personnel and must be contained by expensive means and neutralized. Moreover, spent corrosive liquids must be destroyed by cost-intensive means. The amount of waste materials is thus increased considerably and is a burden on the sewage treatment plant due to the large amounts of salt.